The invention relates to a circuit arrangement for controlling the display of a cursor in a raster-like image, and more specifically for controlling the display of a cursor field of various size.
A circuit arrangement of this kind is known from U.S. Pat. No. 4,354,184 and allows for display of a cursor field of selectable magnitude. This cursor field serves to accentuate an image area in a displayed image, consisting notably of a text to be processed, accentuation being realised, for example by brighter display. No cursor symbol is then displayed in the cursor field.
Also known are circuit arrangements whereby a cursor symbol, for example, an arrow, can be displayed in the cursor field, the parts of the cursor field outside the cursor symbol generally not being visible. The shape of the cursor symbol is determined by the contents of a storage field whose magnitude is defined by the circuitry. In many case the image presents not only the cursor but also characters, i.e. letters and digits whose shape is also determined in storage sections of a memory which may be the same as that for the cursor and which are displayed in character fields of uniform magnitude. The magnitude of a character field then corresponds to the magnitude of the cursor field. In the position in which the cursor is displayed, the pans of the characters displayed in this position in the absence of the cursor are covered, but the cursor may in principle also be at least partly transparent, so that the covered parts of the characters can still be displayed, be it, for example in different colours for background and foreground. When the position data of the cursor indicate arbitrary raster pixels and raster lines of the raster-like image, the cursor field can be adjusted independently of the normally flexed position of the character fields, so that the cursor covers parts of several characters. When the cursor is determined by the display of a fixed symbol, the shape of this cursor symbol can also be changed by erasure or modification of the contents of the storage field determining the cursor shape. The magnitude of the cursor field, however, is always the same.
However, it may be useful to display not only different shapes of the cursor symbol, but also different magnitudes of this symbol. This is not allowed for by the known circuit arrangements for the display of a cursor symbol. In the cited circuit arrangement for displaying a cursor field of variable magnitude, a storage field of variable magnitude with more complex addressing circuitry would have to be used for the display of a cursor symbol of variable magnitude.